Larger Calculations

Here are a few recommendations for carrying out large-basis-set coupled cluster calculations with PSI3:

1. Set the MEMORY keyword to 90% of the available physical memory, at most. There is a small amount of overhead associated with the coupled cluster modules that is not accounted for by the internal CC memory handling routines. Thus, the user should not sepcify the entire physical memory of the system, or swapping is likely.
2. Set the CACHELEV keyword to 0. This will turn off cacheing, which, for very large calculations, can lead to heap fragmentation and memory faults, even when sufficient physical memory exists.
3. Set the PRINT keyword to 2. This will help narrow where memory bottlenecks or other errors exist in the event of a crash.